The objective of this proposal is to study the bulk and adsorptive endocytosis respectively of free horseradish peroxidase (HRP) and ligand-HRP conjugates and their subsequent intracytoplasmic movement in neurons of the central and peripheral nervous system (CNS and PNS) via orthograde and retrograde axonal transport both quantitatively and qualitatively using HRP neurohistochemistry in conjunction with light and electron microscopy in the rat. The relative advantages of different conjugation methods for the preparation of the ligand-HRP conjugates will also be assessed with respect to their influence on the sensitivity of the HRP method used in conjunction with these ligand conjugates. In addition, the feasibility of improving the delivery of the ligand-HRP conjugates to CNS and PNS sites by the use of micropipettes and a hydraulic or electrophoretic injection system will be assessed. The ligands to be evaluated will include the lectins Lens culinaris, Wheat germ agglutinin, Risinus communis I and II, Soybean, Ulex and Lotus as well as the bacterial toxin cholera toxin. The different conjugation methods employed for the preparation of the ligand-HRP conjugates will use glutaraldehyde, p-benzoquinone and periodic acid. The ability of each of the ligand-HRP conjugates to retrogradely label neurons compared with that of free HRP will be quantitatively determined at the light microscope level in 5 different interconnected portions of the CNS and PNS i.e., dorsal lateral geniculate nucleus-striate cortex, locus coeruleus-cerebral or cerebellar cortex, dorsal root ganglion-transected sciatic nerve, hypoglossal nucleus-tongue and superior cervical ganglion-submandibular gland. Electron microscopic observations will be made of cellular "lesions" produced by any ligands and of the neuronal organelles involved in the movement and disposition of the HRP-ligand conjugates compared with that of free HRP. These studies have implications for neurobiology and the application of the HRP method as well as for the ultrastructure of the neuropathological effects of lectins and toxins.